Most of conventional magnetic recording media are of the coated type and are produced by dispersing particles of magnetic oxides or ferromagnetic alloys such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a Berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 and CrO.sub.2 into an organic binder such as a vinyl chloride/vinyl acetate copolymer, a styrene/butadiene copolymer, an epoxy resin or a polyurethane resin, applying the resulting coating solution to a non-magnetic base, and drying the coating.
With recent demands for higher density recording, research has been directed to magnetic recording media of the thin metal film type which uses a thin ferromagnetic metal film as a magnetic recording layer, the same being formed by vapor deposition, such as vacuum deposition, sputtering or ion plating, or plating such as electroplating or electroless plating. Various efforts are being made to use such recording medium on a commercial scale.
Most magnetic recording media of the coated type uses a metal oxide with low saturation magnetization as the magnetic material, so attempts to achieve high density recording using a thinner magnetic recording medium results in a decreased signal output. However, with magnetic recording media of the thin metal film type, a very thin magnetic recording layer can be formed using a ferromagnetic metal having higher saturation magnetization than that of a magnetic oxide without using a non-magnetic material as a binder, and such thin materials are advantageous for providing good electro-to-magnetic conversion characteristics.
However, thin metal film type magnetic recording media have their own problems: (1) high friction against magnetic heads, guide poles or other transport means in recording reproduction devices such as video tape decks, audio tape decks or copiers, which leads to high device wear; (2) ease of attack by corrosive environments; and (3) the magnetic recording layer can be damaged by impact during handling.
Attempts have been made to overcome these problems by forming a protective layer on the magnetic recording medium of thin metal film type.
One proposal is set out in Japanese Patent Application (OPI) No. 75001/75 (the term OPI as used herein means an unexamined published Japanese patent application) where a thin lubricant layer is formed on the metal film. Per this proposal, the coefficient of friction between the magnetic head or guide poles and the metal film is reduced so the tape runs consistently and is not likely to be abraded. However, these advantages are lost if the tape is used repeatedly. Another proposal occurs in Japanese Patent Application (OPI) Nos. 39708/78 and 40505/78 where a protective lubricant layer of a metal or metal oxide is formed on the thin metal film. However, even in this case the effect of the protective layer is short term, and as the tape is used, the friction coefficient rapidly increases or the thin magnetic metal film breaks.
Yet another proposal occurs in Japanese Patent Application (OPI) No. 155010/79 were an overcoat of a high molecular weight film having a thickness of about 0.2.mu. is formed on the metal film; however, this results in a spacing loss which, in turn, leads to reduced output in high density recording.
To achieve high density recording, most thin magnetic metal films are supported on a smooth base, but no matter how smooth the base is, no lubricating method described above provides a magnetic recording medium having good running properties, especially in high humidity, or high wear resistance.